Method for producing cold flowing of metals



March 26, 1957 J. A. CHAPPUIS 2,786,267

METHOD FOR PRODUCING cow FLOWING 0F METALS Filed Nov. 18, 1952 sSheets-Sheet 1 HEAD MOVEMENT Time in lOOihs of a Second F IG 6 MOVEMENTSPRING ACTION m la INVENTOR John A Choppuis ATTORNEYS March 26, 1957CHAPPU|5 2,786,261

Mamon FOR pnonucmc cow FLOWING 0F METALS Filed Nov. 18, 19.52 3Sheets-Sheet 2 SPRlNG ACT ION PWCH MOVEMENT Distance HEAD MOVEMENT Timein IOOths of a Second MOVE T I0 25 3O SPRlNG ACTION 4O 5O 60 DistanceTime in IOOths of a Second FIG. 8.

I N VENTOR John A. Ghoppuis IIHI ATTORNEYS March 26, 1957 ,4. A.CHAPPUIS I 2,786,267

METHOD FOR PRODUCING COLD FLOWING 0F METALS Filed NOV. 18, 1952 FlG.lI.

3 ,Sheets-Sheet 3 MOVEMENT SPRING ACTION Distance HEAD uovzuem Tlme InI00? of a Second hs FIG.9.

Pressure Tlme F l 6. l0.

. r /A k \-lo %1& 5/ H F |G.|2. INVENTOR John A. Ghoppuis BY Wa i/kATTORNEY6 United States Patent METHOD FOR PRODUCING COLD, FLOWING OFMETALS John Albert Chappuis, Neuchatel, Switzerland; Tilla- MargueriteChappuis, Simone Chappuis, and 324311119 Albert Chappuis, heirs of saidJohn Albert Chappuls, deceased Application November 18, 1952, Serial No.321,199

5 Claims. (Cl. 29-552) This invention relates to the forming of metalarticles by shaping a blank between dies, and more particularly to theforming of such articles by movement or flowing of the metal in a coldstate.

Still more specifically, the invention relates to the shaping of metalarticles in a press in which the movement of one of the dyes iscontinuous and relatively rapid.

An object of the present invention is to devise a method by whicharticles may be shaped from metals such as steel by flowing in the coldstate.

Another object is to devise a method by which such articles may beformed accurately at high speed, thus providing low cost production.

A further object is to develop a method of cold shaping articles fromfiat blanks by which projections of a length many times greater than thethickness of the blank may be formed on its flat face, and the volume ofthe metal displaced by flowing may amount to a substantial proportion ofthe total volume of the blank.

Still another object of the invention is to provide an improved methodfor forming articles from flat blanks by means of which the blank is cutout from a piece of stock and formed into the desired article at asingle stroke of the press.

The achieving of the foregoing objects is rendered possible by reason ofa far-reaching, fundamental discovery which I have made regarding thecold working of metals.

If a sudden impact is applied to a cold metal blank confined within adie cavity, as in an ordinary coining press, it is only possible toproduce projections or raised parts of a height which is relativelysmall, compared to the thickness of the blank.

Attempts which have been made to extrude by impact and in the cold stateeven relatively soft metals show that the pressure, at the moment ofcontact of the movable die or punch with the blank, is enormous. Thus,for tin or lead, 85 to 110 kilograms per square millimeter (60 to 80tons per square inch) is required. Commercially pure aluminum needsabout 115 kilograms per square millimeter (80 tons per square inch), andvarious aluminum alloys require 85 to 170 tons per square inch.

An alloy of other metals, having a hardness of about twenty (Brinell)has been found to require more than 400 tons per square inch.

It has been further found that the impact pressures developed, as abovementioned, amount to about twenty times the elastic limit of therespective metals. Since the elastic limit of the best tool and diesteels is only about four times that of mild steel, it is clear that anyattempt to extrude metal from a confined mild steel blank by impact inthe cold state would result in crushing and breaking down the punch ordie, by reason of the fact that the pressure developed at the moment ofcontact ofthe punch with the confined blank, especially when the punchmoves at relatively high speed, would be many times greater than theelastic limit of the steel of which the toolsare made.

As a result of my researches, it has become apparent that the mostsuccessful way to produce a flowing moveice ment of a confined metalblank in the cold state is to so regulate the speed at which the punchmoves, at the moment of contact with the blank, that the generation ofunduly high stresses which the tools cannot withstand is avoided. Thatis to say, the speed of the punch at, and immediately after the momentof contact with the blank, must be relatively slow or, other words, theapplication of the initial pressure must be controlled.

Such low speed movement of the punch, with controlled increasingpressure on the blank will not, however, alone and of itself, producethe desired flow.

I have discovered that the desired result can be obtained, by slowingdown the punch so as to limit the pressure at the first contact with themetal, then maintaining or increasing this pressure during a definitetime interval, and, at the end of such interval, suddenly substantiallyincreasing the pressure for a brief period.

The preliminary 0r pre-conditioning pressure, above referred to, andwhich is applied for a very brief interval, appears to have the effectof rendering the blank relatively plastic, and of creating aquasi-hydrostatic or quasi-hydraulic pressure within the same. When,therefore, the pressure is immediately thereafter suddenly increased,the relatively plastic metal in the blank flows freely into the openingsor recesses provided in the tools for forming the desired projections orraised parts of the article.

Although, in their broader aspects, not limited to any specificstructure, the method of the invention can be carried out by, and theapparatus of the invention can be embodied in a conventional crank oreccentric press, and, by way of example, and for purposes ofillustration, such a press will be described in the followingspecification.

In order that the invention may be readily understood, reference is hadto the accompanying drawings, forming part of this specification, and inwhich: i

Fig. 1 is a more or less diagrammatic vertical section through the headof a crank-type press modified in accordance with the invention and alsoshowing the punch and die, parts being in elevation, this figureillustrating the position of the parts at the moment of cutting out theblank from the stock;

Figs. 2, 3, 4 and 5 are similar views showing the success1ve positionsassumed by the parts during the com pletion of the stroke of the press;

Fig. 6 is a diagram showing the comparative movements of the head of thepress and of the punch, the diagram also illustrating the action of thespring assembly as the head moves. Theparts of the curves shown in heavyhngszin this figure illustrate the steps shown in Figs. 1 an Figs. 7, 8and 9 are similar diagrams, the heavy portions of the curves in thesediagrams illustrating the steps shown respectively in Figs. 3, 4 and 5.

Fig. 10 is a diagram illustrating the changing pressures exerted on theblank, with respect to time, as the press makes its working stroke; and

Figs. 11 and 12 are fragmentary, vertical sections similar to Fig. 4,but on a larger scale, showing modified construction of the punch andanvil.

Referring to the drawings in detail, and more particularly first to Fig.1 thereof, I have illustrated a press having a head 1 provided withtrunnions 2 to which are attached connecting rods 3 extending to somesuitable eccentric or crank shaft (not shown). The interior of this headis hollow so as to provide a cylindrical chamber and through the centerof this chamber extends a vertical rod 4, sliding freely through thehead and having its upper end threaded to receive a nut 5 which isadapted to engage the head.

The lower end of the rod is rigidly connected with a sweeper screwthreaded block 6 on which works a nut 7 which may be vertically adjustedon the block by turning the same.

To the lower end of the block 6 is secured a punch 8, which cooperateswith and closely fits a hollow die in having a cavity to receive theblah and provided with an anvil 11 which supports the blank in thecavity. It will of course be understood that this die and anvil aresuitably supported on the bed of the machine (not shown) and that meansfor eiecting the finished article from the die (not shown) are alsoemployed.

The apparatus is illustrated as operating upon round disc shaped orcylindrical blanks such as indicated at x, these blanks being cut from asuitable sheet metal stock or strip X. This strip is supported on thetop of the die it) and the blanks are cut out therefrom by the punch 3as it descends. Fig. 1 shows the punch in the act of cutting out such ablank, the blank being shown as partially severed from the stock.

It may be explained here that my improved method relates especially tothe forming of metal articles from relatively small blanks of thisnature having flat faces, and, as a result of my improved method,various kinds of projections or raised parts may be formed on the flatface of the blank. Such projections may be produced on either one orboth faces of the blank and may take the form of either a single columnor stud, or a plurality of such studs or columns, either of the same ordifferent lengths. The invention is also equally well adapted forforming annular portions such as hollow hubs, rims or flanges projectingfrom the flat faces of the blank.

Such projecting parts are formed by providing suitable complementaryopenings or recesses in either the anvil or punch, or both.

For purposes of discussion, and for the sake of simplicity, it will beassumed that it is desired to form an article consisting of a circulardisk or head with a relatively long stem or column projecting centrallyfrom one. face. For producing an article of this kind, the punch S isformed with a central opening or recess 9 extending axially thereof. Aspressure is applied to the blank by the punch in accordance with thepresent invention, the metal of the blank is caused to flow up into thisopening 9, thus producing the desired article.

Enclosed within the chamber of the head, and interposed between thescrew threaded block 6 and the top wall of such chamber, is a suitablespring assembly which bears resiliently against the screw threaded block6, it being understood that this block is of such a size as to becapable of entering the chamber in the head 1 and moving freely withrespect thereto. Although other types of springs might be employed, 1have illustrated a group of what are known as Belleville rings orwashers 12. These surround the rod 4 and occupy the annular spacebetween this rod and the walls of the cylindrical chamber in the head.

Each of these rings or washers is similar in shape to an ordinary saucerwith the center portion cut out. Single rings may be assembledalternately face to face and back to back, so as to form an axiallycompressible stack, or they may be assembled in nested pairs, asillustrated in the drawing, or in any other desired nested groups, suchgroups being arranged alternately face to face and back to back. Whenthe stack is compressed, the individual rings or washers tend to flattenout, as will be obvious. These rings or washers are of course made ofstiff spring steel, so that they are extremely resilient and elastic,being distorted or flexed by heavy applied pressure, and immediatelyreturning to their original shape when the pressure is removed. They arepreferably so designed that relatively small increases in appliedpressure will produce a substantially increased distortion.

The multiple groupings above mentioned are referred to as seriesparallel arrangements, and are identified by code numbers. Thus 5 x 2would mean an assembly of five pairs or groups of two, as shown in thedrawings. 6x4 would mean an assembly of six groups of four each, therings of each group being nested, etc. It is obvious that by using morenested units in each group, the stiffness or resistance of the assemblyis increased, and by using more groups the possible amount of deflectionor compression of the stack is increased.

in the arrangement illustrated in the drawings, the spring assembly,when the press is idle, is under but little it any compression. Inpractice, however, it may often be desirable to put the spring assemblyunder substantial compression at the start, or, in other words, topre-load the springs. This can be accomplished, to any extent desired,by screwing down the nut 5, thus drawing block t; more or less up intothe chamber of the head. Pro-loading the springs in this way results inrendering the assembly stiffer, and in reducing the amount of possiblefurther compression.

As the head of the press makes its downward stroke, and the punchengagesthe stock X, the first effect is to compress the spring assembly12, thus forcing the block 6 up into the cavity of the head to someextent as crlown in Fig. 1. The springs are made of such strength thatthe elastic pressure which they exert on the punch is suilicient tocause it to cut the blank out of the stock. Immediately after the blankis cut out, as shown in Fig. 2, the pressure is relieved and the springsexpand, thus forcing the block 6 downwardly out of the cavity in thehead. The next instant, however, the punch enters the die cavity andengages the blank as shown in Fig. 2. Thereupon, as the head continuesto descend, the springs 12 become more and more compressed, as the blockmoves further and further up into the cavity in the head, as shown inFig. 3.

After the head has moved slightly further down than shown in Fig. 3,the. bottom of the head engages the top of thenut 7 as shown at 13 inFig. 4. No further compression of the springs is thereafter possible,but from this instant the punch is solid or rigid with the head andmoves downwardly with it.

From the foregoing, it will be seen that as the punch engages the blank,as shown in Fig. 2, and the head con tinues to move downwardly, thepunch does not move downwardly at the speed of the head, but itsmovement is slowed or delayed by reason of the yielding or deflection ofthe spring assembly 12. In other words, at the moment of contact betweenthe punch and the blank, the speed of the punch becomes less than thatof the head, and from this point onward until. the parts reach theposition shown in Fig. 4, the punch exerts a gradually increasingelastic pressure on the blank as the spring assembly 12 is more and morecompressed.

Finally, when the position of Fig. 4 is reached, and the punch becomesrigid with the head, a suddenly increased pressure or solid thrust isapplied to the punch and blank.

It appears that the first effect of applying the yielding or elasticpressure to the blank, beginning with the position of the parts as shownin Fig. 2, and thereafter gradually increasing, is to cause the blank tocompletely and absolutely fill the cavity of the die in which it isconfined. It further appears that this application of pressure on theconfined blank creates a quasi-hydrostatic or quasishydraulic pressurewithin the blank itself, which hydrostatic pressure, maintained during adefinite, controlled time. interval, renders the metal of the blankrelatively plastic. At the end of the period of application of elasticpressure, or, in other words, when the elastic pressure has reached itsmaximum, the blank has been rendered plastic to such an extent that itwill usually begin to flow into the opening or recess 9 of the punch, asindicated at y iii-Fig. 3, but if the operation should be stopped atthis stage; no satisfactory movement of metal would be produced;

' Whemhowever, at the next instant, the nut 7 engages the head 1, thusrigidly coupling the punch to the head, a sudden increase of pressure isdeveloped and delivered to the already plastic blank and this increasedpressure results in causing the metal of the blank to freely flow upinto and fill the opening in the punch as shown at z in Fig. 4.

It will thus be seen that I achieve this remarkable flowing of the metalin a cold state by first generating in the blank a kind of hydrostaticpressure, thus rendering it relatively plastic and then, at the properinstant, suddenly subjecting the plastic blank to a positive force whichcauses the metal to move freely into the opening in the punch.

To look at it another way, during the time that the spring assembly isbecoming more and more compressed, as the head moves downward, the punchis slowed up and lags behind the movement of the head. When, however,the head engages the nut 7, and the punch thus becomes rigidly coupledto the head, the punch is given an accelerated further movement, at thespeed of the head. While, during the previous time interval, the punchhad been exerting a yielding pressure on the blank, at the instant ofcontact of the head with the nut 7, the punch applies a positive,unyielding thrust to the blank.

In the embodiment shown, the pressure applied to the blank through thespring assembly is a yielding, gradually increasing pressure. The factthat this pressure is gradually increasing is inherent in the particulartype of press illustrated, but is by no means essential to theinvention. So far as the improved method is concerned, the appliedpressure might be uniform during the definite time interval abovementioned.

There are, in fact, two time intervals involved in my improved method,namely the interval during which the preliminary or pre-conditioningpressure is applied, and the interval during which the actual flow takesplace. The first, although on the order of a few hundredths of a second,is relatively longer than the succeeding interval. The first isadjustable, the second is not, but determined by the existing physicalfactors.

7 With a given speed of the press, the duration of the first intervalmay be adjusted or controlled by selecting any desired number of ringsto make up the spring assembly, and by pre-loading the assembly to anydesired extent by means of the nut 5. The duration of the secondinterval, however, is determined by the speed of the press, thethickness of the blank, and the amount of displacement of the metal. Itwill be understood that the setting of the spring assembly as abovementioned, controls both the magnitude of the initial pressure, and alsothe length of the time interval through which it is applied.

It should be explained that the clearance necessary between the punchand anvil of the die when the punch reaches its extreme position at theend of its stroke, varies in accordance with the original thickness ofthe blank and the amount of metal to be displaced, or, in other words,with the final thickness of the blank after the article has been formed.This clearance may be controlled as desired, either by making the punch8 longitudinally adjustable with respect to the block 6, or by adjustingthe height of the anvil by means of suitable shims. It has not beendeemed necessary to illustrate this in the drawings, since it isbelieved to be obvious.

Referring now to Figs. 6-9, I have attempted to show diagrammatically. acurve :1 indicating the movement of the press head and a curve bindicating the corresponding movement of the punch. In thesefigures, Ihave also attempted to incorporate a third curve 0 showing the action ofthe spring assembly. It will be understood that these are time-distancecurves and, for'purposes of illustration, the speed of the press isasserned to be such that it makes a'completestroke in 9 of a second.

The curve a, showing the movement of the head, is a simple sine wave,since the head moves with a regular harmonic motion as the crankrotates. The punch, however, does not describe a simple harmonic motion,due to the fact that the inter-position of the spring assembly 12 causesit to lag behind the head at some points.

The portion b of the curve b, as illustrated in Fig. 6, shows how thepunch is slowed down by engagement with the stock as shown in Fig. l,and it is then freed and moves suddenly at increased speed as it cutsthrough the stock and the springs expand as shown in Fig. 2, and asindicated by the portion b of the curve.

In this Fig. 6, the portion 0 of the curve a shows the gradualcompression of the spring assembly as the punch encounters the stock inFig. 1, the portion 0 of the curve indicating the sudden relaxing of thespring pressure as the punch goes through the stock as in Fig. 2.

In Fig. 7, the portion b of the curve b shows how the punch is delayedor slowed down as it imposes a gradually increasing pressure on theblank as the springs are compressed up to the position shown in Fig. 3.It will be particularly noted that the portion b of the curve is by nomeans parallel with the corresponding portion a of the curve a, sincethe downward movement of the punch during this interval is much lessthan the downward movement of the head. Similarly in Fig. 7 the portionc of the curve 0 shows how the spring assembly is progressivelycompressed as the head moves down.

Fig. 8 illustrates the step of the operation shown in Fig. 4 in whichthe block 6 and head 1 are rigidly coupled together and in which thepunch moves at the same speed as the head. In this figure the portion bof the curve b is substantially parallel with the corresponding portiona of the curve a, showing that the punch and head move together duringthis brief period. In the same figure, the portion 0 of the curve 0 is astraight hori zontal line, showing that there is no further compressionof the spring assembly during this period. The punch remains rigidlycoupled to the head until after the lower dead center of the crank isreached as indicated at a which point is shown as substantially on thevertical line 30, which marks the middle of the stroke.

Referring finally to Fig. 9, this illustrates what happens as the crankpasses dead center and the head begins to rise. The portion b of thecurve b at this point again does not follow the corresponding portion aof curve a, because, at this instant, the spring assembly is relaxingand holds the punch down for a short time after the head begins to rise.Also, in this figure, the portion of the curve 0 shows how the springassembly expands as the head moves up. After a brief instant, thesprings have fully expanded, as shown in Fig. 5, and remain in thiscondition during the completion of the stroke.

Referring now to Fig. 10, I have endeavored by means of a time-pressurediagram to illustrate in a general way the variations of pressure towhich the blank is subjected during the stroke of the press. The point:1 of this curve d represents the maximum pressure at the instant whenthe punch cuts through the stock as shown in Fig. 1, and the curve thendrops away showing that the pressure is relieved at the instant that theparts occupy the position shown in Fig. 2. From this point, a graduallyincreasing pressure is applied to the blank as indicated by the portiond", and this continues until the point d is reached at which the headbecomes rigid with the punch as shown in Fig. 4. At this moment, thereis a sudden increase of pressure applied to the blank as indicatedby'the portion d of the curve. The exact shape of this part of the curveis pr'oblematical. At the moment at which the punch becomes rigidlycoupled to the head, the pressure rises abruptly, but, as the punchcontinues its downward movement, and the metal flows, as described, itseems probable that this flowing may relieve, or at least limit thepressure. The diagram shows the pressure curve rising vertically to amaximum, and then flattening out, as indicated at d while flowing takesplace. This pressure is maintained substantially until dead center isreached. The portion 0' of the curve indicates how the pressure on theblank is prolonged for a brief period by the expansion of the springassembly immediately after the dead center is passed. After this briefperiod the pressure of course immediately falls away to zero.

When working with flat blanks of the character described, tests showthat the metal layer in contact with the recessed tool does notcontribute to the formation of the raised parts or projections. T hedeeper or intermediate layers, on the contrary, supply the metal toprovide the projections. This metal fiows at first in a directionparallel to the faces of the blank and afterwards bends to a directionat right angles and flows into the opening or recess in the tool. 1

During the deformation of the blank, 21 certain amount of heat isgenerated, thi heat assisting somewhat in keeping the metal malleableand tending to prevent the hardening effect which is sometimes noticedin the cold working of metals.

With soft metals, extrusion may be obtained with little difiiculty dueto the fact that the stresses necessary to deform these metals veryquickly and cause the blank to completely till the cavity of the die donot exceed the resistance of tool steel. When working steel, however, alonger time is necessary to obtain this result, and for this reason myimproved method includes the step of slowingdown the speed of the punchat the moment it comes into con tact with the blank so as not togenerate unduly high stresses in the tools. The desirable speed is afunction of the elastic limit of the particular metal, and the higherthe elastic limit, the lower the speed of the punch should be.

Not only must the speed be lower, the higher is the elastic limit of themetal, but the speed must remain low for a longer time the more theshape of the blank differs from the shape of the cavity in the die, thatis to say, a longer time is needed to obtain the quasi-hydrostatic orquasi-hydraulic pressure in the metal, above referred to. Once thiscondition of hydrostatic pressure is produced, however, the deformationor flowing must then be performed rapidly.

As above mentioned, my improved method comprises limiting the pressureon the blank at the first contact of the punch with the metal, and thenmaintaining or increasing this pressure. In the embodiment illustrated,the pressure is increased due to the fact that the elastic assembly ismore and morecompressed. It is during this period, the duration of whichis of the order of some hundredths of a second, that the blank is causedto completely conform with the shape of the cavity in which it isconfined. Immediately afterwards, when a state of quasi-hydrostaticpressure has been reached Within the blank, 2. positive flowing pressureis applied to obtain the desired displacement of the metal. At thispoint, it is no longer necessary to limit the speed at which the punchmoves. On the contrary, the flow of metal will be more substantial ifthe speed is relatively high.

In practice, and with a press of the type described, the extent ofslowing down of the punch and the duration of the period in which theincreasing elastic pressure is applied, is regulated by varying thecharacteristics of the spring assembly. The fewer Belleville rings orwashers employed, the less will be the slowing down of the punch and theshorter will be the time interval during which elastic pressure isapplied. if it is desired to increase the time interval, a greaternumber of rings or washers is employed. The time interval may also beshortened by pre-loading the spring assembly by screwing up the nut 5,as above explained.

Tests were carried out with a crank type press running. at a speed of100 strokes per minute, and with a 60 mm.

stroke, on blanks of mild steel having a diameter of 11.5

to of a second.

mm. and a thickness of 3 mm. and with a punch closely fitting the'diecavity and having an opening or recess the diameter ofwhich was about22% of the diameter of'the blank. With these dimensions, it will be seenthat the blank wasconfined within the die cavity over about 98% of itstotal surface While the exact percentage will of course vary with thenumber and size of the openings in the tool, the essential thing is thatthe blank be confined over a major portion of its surface. When nosprings at all were used, the metal of the blank entered the opening fthe punch to the extent of only 0.3 mm. When a 2 x 4 spring assemblyhaving a short time interval and a very small elastic deformation suchas 2.2 mm. was used, nearly the same result was obtained at the end ofthe l'sation of yielding. pressure, not followed by any rigid couplingof the punch to the head. When the press was so arranged that at the endof the application of the yielding pressure, the punch became rigidlycoupled to the head, as shown in Fig. 4, a plug or column was forcedinto the opening-of the punch to a height of 1.5 mm.

When a 4 x 4 spring assembly capable of an elastic deformation twice aslarge as that above referred to, namely, about 4.4 mm. was employed, aplug of about 3.2 mm. was obtained.

Using a 6 x 4 spring assembly having a still greater elasticdeformation, namely, a deformation of about 6.6 min, three times thatreferred to in the first example, it was possible to obtain a plug orcolumn 4.1 mm. in height.

Experiments have shown, however, that increasing the elastic deformationof the spring assembly beyond this point, that is to say, still furtherlengthening the time interval during which the preliminary pressure isapplied, does not improve the results, but, in fact, is a disadvantage.Thus, when the elastic deformation of the spring assembly was increasedto four times that of the first example, namely, to 8.8 mm, a plug orcolumn of only 3.1 mm. in height Was obtained. Further increasing theelastic deformation by another 25%, yielded a plug of only 2.6 mm. inheight. There appears to be therefore an optimum amount of elasticdeformation or, in other words, an optimum time interval during whichthe elastic pressure is applied, this optimum producing a maximum flow.Such an optimum depends, among. other things, upon the nature andhardness of the metal and can be calculated or predetermined for anyparticular kind of metal, and the amount of displacement to be produced.

Although, as indicated by the diagrams'of Figs. 6l0, the time, duringwhich the elastic pressure was applied to the blanks, is shown as aboutof a second, such time may vary from 5 to of a second, while the periodduring which the punch moves rigid with the head and subjects the blankto a positive flowing pressure is usually considerably less, namely, onthe order of 1 In practice, the time intervals will vary, depending uponparticular conditions such as the size and hardness of the blank, theamount of displacement to be produced, etc.

The exact point of transition between the application of elasticpressure and the rigid coupling of the punch to the head can be selectedas desired by adjusting the position of the nut 7 on the block 6, and inthis way the relative lengths of the respective time periods for the twophases of the operation may be altered at will.

As to the actual amount of pressure necessary, it has been found thatmild steel blanks of a hardness of 100 to 115 Brinnell and having asurface of 100 to square millimeters required a maximum elastic pressureof about 17 tons, that is to say, a pressure of about 200 kilograms persquare millimeter.

The size and stiffness of the spring rings necessary to provide thedesired amount of pressure, can be determined by tests, or may beascertained from the manufacturer-s ratings.

The percentage of metaldispla'ced by my improved in -w method isrelatively large. For mild steel blanks, and working with a punchclosely fitting the die cavity and having an opening of a diameter of22% of the diameter of the blank, the metal displaced or caused to flowinto the opening was about 28% of the total initial volume of the blank.When the die or punch had a number of holes or openings instead of one,and where the thickness of the blank did not exceed 25% of its diameter,still greater displacements have been obtained.

While, for the sake of simplicity, the foregoing description has beenbased upon an imperforate anvil and a punch having a single opening,thus producing an article consisting of a flat head and single, longshank or stem, the invention is not, of course, limited to suchconfigurations but is applicable to articles of a wide variety ofshapes.

Thus, for example, in Fig. 11, I have illustrated the making of anarticle consisting of a disk having a plurality of projections or stemsZ Z2, on one face, and one or more projections 5, on the other face. Inthis case, an aperture or recess is formed in the anvil 11 to producethe lower projection.

In Fig. 12, I have illustrated the making of an article having on oneface a peripheral flange and on the other face, a central projection Z5.In this case 1 pro vide the punch 8 with an annular groove to form theflange, instead of with an opening.

Where a number of projections are thus formed on one or both faces ofthe blank, it is possible to displace even a larger percentage of themetal than in the case of a single projection, but the projections, ofcourse, will not be as long.

While, by way of example, I have illustrated the blank as a circulardisk, it will of course be understood that the invention is equallyapplicable to the formation of articles from square or other polygonalblanks.

What I claim is:

1. The method of forming a metal article from a discshaped metal blankof substantial thickness in a cold, rigid state comprising confining theblank in a die cavity between an anvil and a punch, one of said partshaving an opening extending at substantial right angles to the plane ofthe disc, subjecting said confined blank, by means of the punch, to apreliminary elastic pressure, gradually increasing this pressure duringa definite time interval of a few hundredths of a second until the metalof the blank becomes relatively plastic and begins to flow into saidopening, and thereupon suddenly exerting on said confined, relativelyplastic blank, by means of said punch, an unyielding thrust, to causethe metal to flow further into said opening to form on the blank aprojection of substantial length.

2. The method of forming an article from a disc-shaped steel blank ofsubstantial thickness in a cold state comprising confining the coldblank in a die cavity between an anvil and a punch, one of said partshaving an opening, causing said punch to apply an elastic pressure tosaid confined blank, gradually increasing such pressure during a timeinterval of a few hundredths of a second until it reaches a value on theorder of two hundred kilograms per square millimeter and the steelbegins to flow into said opening, and immediately thereafter causingsaid punch to exert a suddenly increased, unyielding pressure on saidconfined blank, whereby the steel is caused to flow further into saidopening to form on the blank a projection of substantial length.

3. The method of forming an article from a disc-shaped steel blank ofsubstantial thickness in a cold state cornprising confining the coldblank over approximately ninety eight percent of its total surface in adie cavity, subjecting the confined blank to a preliminary elasticpressure for a few hundredths of a second until the metal of the blankreaches a state of such relative plasticity that it is caused to conformto and completely fill the cavity of the die, and thereupon suddenlyincreasing such pressure by applying an unyielding thrust, whereby therelatively plastic metal of the blank is caused to flow out over theapproximately two percent of its surface which is not confined.

4. The method of forming an article from a discshaped cold metal blankin a press having a punch and a. die, such method comprising causing thepunch to perform three consecutive steps at a single stroke, namely,first, by its initial movement, to cut the blank from sheet metal stockand force it into the die, second, by a further movement in the samedirection, to exert a gradually increasing elastic pressure on theconfined blank until it conforms to and completely fills the die cavity,and third, by a final movement in the same direction to exert on theblank a sudden, unyielding thrust to produce the desired deformation,all three steps being performed within a total time interval of afraction of a second.

5. The method of forming an article from a solid steel blank in a cold,rigid state, said blank having a flat face, comprising confining over amajor portion of its surface the cold blank in a die cavity between ananvil and a punch closely fitting said die cavity, one of said partshaving an opening extending at substantial right angles to said fiatface of the blank, subjecting the fiat face of the confined blank to acontrolled preliminary pressure on the order of two hundred kilogramsper square millimeter by means of the punch, maintaining such pressurefor a few hundreths of a second until the steel of the blank reaches astate of such relative plasticity that it is caused to conform to andcompletely fill the cavity of the die and to enter said opening to aminor extent, and thereupon suddenly increasing the pressure applied bysaid tool on the flat face of said confined, relatively plastic blank tosuch 'a. degree as to cause a major flow of the steel into said opening.

References Cited in the file of this patent UNITED STATES PATENTS850,212 Conlen Apr. 16, 1907 1,063,632 White June 3, 1913 1,380,250Reymond May 31, 1921 1,484,490 Goldschmidt Feb. 19, 1924 1,921,654Burbank Aug. 8, 1933 1,955,243 Liebergeld et a1. Apr. 17, 1934 2,125,068Dempsey July 26, 1938 2,135,803 Dumert Nov. 8, 1938 2,162,132 Spire June13, 1939 2,225,345 Lemoreaux Dec. 17, 1940 2,241,735 Redsecker May 13,1941 2,261,304 Sparks Nov. 4, 1941 2,382,045 Flowers Aug. 14, 19452,432,717 Berger Dec. 16, 1947 2,473,371 Heath et a1. June 14, 1949FOREIGN PATENTS 698,303 France Nov. 17, 1930 OTHER REFERENCES Iron Age,pp. 69-75, Oct. 19, 1950. Wall Street Journal, page 5, Sept. 20, 1951.

